Conventional flares are not re-usable: once lit they burn for approximately twenty minutes. They are a constant fire hazard when lit and so their use is somewhat limited. The fire hazard persists to some extent even after the flare is burned out and so it must be disposed of carefully. Electronic strobe flares are available but they are relatively expensive, large and heavy and tend to short battery life. In addition, the flash mechanism is often quite delicate and usually provides only unidirectional output.